This invention relates to cargo-handling apparatus for use on containerships. More particularly, the invention relates to apparatus for securing stacks of containers carried on the deck of a containership.
The advent of the container has pointed the way to potentially great savings in time and labor in handling cargos. Realizing that potential, however, has required the development of specialized apparatus for transporting and handling containers. The most dramatic development has been the evolution of the containership, with attendant port facilities designed specifically for rapid handling of containerized cargo. Such ships not only carry containers in their holds, but also containers may be stacked on deck, permitting maximum utilization of available space.
On-deck containers present several problems. First, the stacks of containers must be fixed securely in position, to prevent their movement--and resulting damage--during the pitching and rolling to be expected during an ocean voyage. Second, the means employed to secure the containers must be easy to use, to permit rapid loading and unloading; otherwise, the potential for savings of time and effort will be lost. Third, a securing apparatus should not unduly raise the ship's center of gravity. Ideally, the securing apparatus should be lightweight and low to the deck, allowing containers to be stacked to the maximum height consistent with ship stability; short of the ideal, every effort should be made to keep the apparatus as low as possible. Fourth, the apparatus must be reliable and maintenance-free. In an environment where containers, hatch covers, and other equipment typically are handled by cranes, the apparatus cannot be prone to damage or downtime.
The original method for securing containers is by lashing. The bottom container of a stack is placed on deck--or, more specifically on a hatch cover, as hatch covers form the most convenient deck area for storage--with its corners engaged by castings, which restrain side-to-side movement. Vertical locating apertures are fitted in the corners of the container top and bottom, and horizontal locating apertures similarly are located in the corners of the ends and sides. Dowels placed in the vertical locating apertures atop one container engage similar apertures in the bottom of a subsequent container, to prevent side-to-side movement. The entire stack is then held in place by lashings fitted with turnbuckles and the like. Obviously, rigging such lashings is highly labor intensive and consumes valuable dockside time. Also, lashings require frequent inspection and maintenance during a voyage and must be replaced frequently.
Some of the disadvantages of lashings are overcome by providing stacking frames in lieu of lashings. Most such apparatus is bulky and must be moved into place by cranes, however, considerably lengthening the time required to on-load and off-load a ship. In addition, the frames commonly in use result in a higher stack of containers, often raising the ship's center of gravity unacceptably. For example, one typical stacking frame system results in a container stack 1.2 feet higher than the stack would be if lashed in place. Even such a seemingly small difference in center of gravity can result in the ship becoming marginally unstable; in such a situation, there is no choice but to leave cargo behind.
Another system employs fixed cell guides on deck. Such guides must be located so that containers fit snugly against guide rails. Because containers usually are stacked on hatch covers, however, the cell guides must overlap onto them, resulting in considerable difficulty in removing the hatch covers. One is faced with a choice of employing fixed cell guides and accepting a high level of damage during hatch cover removal, or employing removable cell guides, which require additional time during loading and unloading to erect and dismantle the guide systems.
A disclosure by Tabuchi, U.S. Pat. No. 3,680,518, attempts to solve these problems by providing apparatus comprising pillars located adjacent the hatch covers, carrying swinging arms with pins which engage the container locating apertures. A pivot arm is provided for each container in a stack, including the top one. This system possesses two major disadvantages. First, it does not overcome the problem encountered by cell guides in that the swinging arms, even in their retracted position, are vulnerable to damage during removal of a hatch cover. One can imagine the difficulty of lifting a heavy hatch cover past successive rows of projecting apparatus; the slightest shift in the wind or the smallest mistake by the crane operator will result in the hatch cover swinging and smashing against a projecting arm mechanism, crushing it. This system inherently is prone to high downtime due to damage. Also, the necessity for a pivoting arm apparatus atop the uppermost container raises the ship's center of gravity. An effective system should avoid placing heavy apparatus at such a great distance from the deck.
Thus, the result of considerable effort in the prior art has not produced apparatus which meets all of the criteria outlined above. The container shipping industry remains in need of effective, easy-to-use, compact means for securing on-deck containers.